The present invention relates to a fiber optic module which can be used in such a device as to perform data transfer between apparatuses.
There has been so far known such a fiber optic module as shown in FIGS. 17-19 (disclosed in JP-A-3218134). FIG. 17 is a plan view of a prior art fiber optic module which comprises laser diode (LD) modules 1 for transmitting an optical signal onto a printed circuit board 3 having a width of 76 mm and a length of 75 mm, photodiode (PD) modules 2 for receiving the optical signal, semiconductor ICs 4 and 5 for converting the optical signal into an electric signal, and a connector 6 for transfer of the electric signal to a mother board (not shown in the drawing).
FIG. 18 is a cross-sectional view of a major part of a lower frame for the prior art fiber optic module. The prior art fiber optic module is fixed to the mother board (not shown) by means of a spacer 8 and a J-letter shaped clip 9 both formed in a lower frame 7b.
FIG. 19 is a cross-sectional view showing a holding mechanism of the prior art fiber optic module to be held to the circuit board. More specifically, the circuit board 3 is inserted into a rear part of the lower frame 7b and then held by the upper and lower frames 7a and 7b.
However, the above prior art has had several problems which follow.
1) The electric signals are transferred on a parallel data basis, and then even though each of parallel signals consists of, e.g., 8 bits, the number of signal lines transferring the parallel signals as well as other signals becomes as many as 50, which requires the large size of connectors and semiconductor ICs for serial/parallel conversion, which results in that the size of the entire unit must be inevitably made large. Further, not only the large size of this unit per se goes against a recent tendency of the rapid downsizing movement of host computer but this also largely limits the design flexibility of mother board for system manufacturers.
2) The fixation between the fiber optic module and mother board in the prior art is effected by means of the J-letter shaped clip 9 in the form of a resin leg extended from the lower frame 7b as already explained in connection with FIG. 18. This requires a large hole as an opening for fixation in the mother board, whereby the design flexibility of the mother board by the system manufacturer is largely limited. Further, since the prior art has such a structure that a load caused by the force derived by mounting and dismounting of the optical fiber is applied to the J-letter shaped clip 9 and the lead (not shown) of the connector 6, this causes a breakage of the J-letter shaped resin-clip 9 made from resin or a poor connection of the connector lead, with the result of reduction in the reliability of the fiber optic module.
Furthermore, for the purpose of avoiding any stress applied to the leads of the LD modules 1 and PD modules 2, the accuracy of each of the parts must be increased and thus parts management (such as parts acceptance inspection) becomes necessary, which make it difficult to obtain a low-cost fiber optic module.
3) The prior art fiber optic module is fixed by soldering the connector 6 to the circuit board 3 and thereafter the signal lines of the connector 6 are directly connected to the mother board by soldering. The necessity of these works hinders realization of a low-cost fiber optic module.
4) In the method for holding the circuit board 3 as shown in FIG. 19, a warpage occurs in the circuit board 3, which remarkably deteriorates the reliability of the circuit board 3. Further, the holding method shown in FIG. 19 requires a sufficient length of the circuit board 3 itself and a sufficient circuit-board holding length L, which hinders realization of a miniaturized fiber optic module.
5) Since most area of the circuit board 3 is in its exposed state, when a worker handles the prior art fiber optic module or a user mounts the prior art fiber optic module onto the mother board, the prior art fiber optic module is susceptible to electrostatic destruction, which leads to poor reliability and costliness of the fiber optic module.
6) During a long-term storage, dust or foreign matter invades into the LD and PD modules into which optical fibers are to plug, which causes improper or poor connection between the optical fiber and the module, thus resulting in remarkable reduction in the reliability of the fiber optic module.